1. Field of the Invention
The present invention relates to a magnetic tape and a magnetic recording device comprising the same. More particularly, it relates to a magnetic tape affording good electromagnetic characteristics, good running durability and good running stability, and to a magnetic recording device comprising the same.
2. Discussion of the Background
As the quantity of recorded information has increased, ever higher recording densities have been demanded of magnetic recording media. Accordingly, to achieve high-density recording, the practice of increasing the fill rate of the magnetic layer by using microparticulate magnetic powders has been widely employed.
Conventionally, primarily ferromagnetic metal magnetic particles have come to be employed in the magnetic layer of magnetic recording media for high-density recording. However, a limit has begun to appear in the improvement of ferromagnetic metal magnetic particles to achieve higher density recording. By contrast, the coercive force of hexagonal ferrite magnetic particles is great enough for them to be used in permanent magnetic materials. Their magnetic anisotropy, which is the basis of this coercive force, derives from their crystalline structure. Thus, it is possible to maintain the coercive force even when the particles are reduced in size. Further, magnetic recording media with magnetic layers in which hexagonal ferrite magnetic particles are employed can exhibit high-density characteristics based on the vertical component. Thus, hexagonal ferrite magnetic particles are a ferromagnetic magnetic material that is suited to achieving higher densities.
However, since hexagonal ferrite magnetic materials are tabular in form, in contrast to ferromagnetic magnetic particles, which are acicular in form, and since they have an easily magnetized axis in a direction perpendicular to the tabular surface thereof, they tend to undergo stacking (a state where the magnetic particles aggregate like the beads of an abacus). When the magnetic particles aggregate, a state similar to that of coarse particles being present in the magnetic layer is created, even with microparticles. The noise increases, causing the SNR to drop. As a countermeasure, attempts have been made to prevent aggregation (stacking) of the particles by increasing the dispersion of hexagonal ferrite. In this context, reference can be made to Japanese Unexamined Patent Publication (KOKAI) Heisei No. 4-178916 (Reference 1), Japanese Unexamined Patent Publication (KOKAI) Heisei No. 5-283218 (Reference 2), Japanese Unexamined Patent Publication (KOKAI) Heisei No. 5-144615 (Reference 3) or English language family members U.S. Pat. Nos. 5,378,547 and 5,494,749, Japanese Unexamined Patent Publication (KOKAI) No. 2002-298333 (Reference 4) or English language family members US 2003/049490A1 and U.S. Pat. No. 6,689,455 B2, and Japanese Unexamined Patent Publication (KOKAI) No. 2009-099240 (Reference 5) or English language family member US 2009/098414 A1, and Japanese Unexamined Patent Publication (KOKAI) No. 2002-373413 (Reference 6), which are expressly incorporated herein by reference in their entirety.
Further, when the particle size of the magnetic particles is reduced, running durability decreases (the output fluctuates with repeated running) and running stability deteriorates. These are thought to be caused by a drop in the film strength due to a reduction in the size of the magnetic particles. Such phenomena should be avoided, particularly in data backup tapes that are required to maintain high reliability for long periods. Accordingly, various investigation has been conducted into improving the running durability and the like of magnetic recording media. For example, the control of protrusions (see Japanese Unexamined Patent Publication (KOKAI) No. 2005-243162 (Reference 7), which is expressly incorporated herein by reference in its entirety) by means of abrasives, the use of binder of high Tg (see Japanese Unexamined Patent Publication (KOKAI) No. 2004-319001 (Reference 8) or English language family member US2004/219393 A1 or U.S. Pat. No. 6,991,862 B2, which are expressly incorporated herein by reference in their entirety), and the like have been proposed.